1. Cross-reference to a Related Application
Reference is made to commonly assigned copending patent application Ser. No. 420,078, filed simultaneously herewith in the name of Douglass L. Blanding and entitled SUPPORT MEANS FOR ELECTROPHOTOGRAPHIC FILM CORE AND ASSOCIATED ELEMENTS.
2. Field of the Invention
The present invention relates to electrophotographic copying or printing machines and, more particularly, to a film core device for supporting and guiding a photoconductor belt in such a machine.
3. Description Relative to the Prior Art
Many electrophotographic copiers or printers employ an endless photoconductor belt rather than a photoconductor drum and the device that carries the photoconductor belt, including the belt-supporting rollers, is commonly referred to as a film core.
Because the photoconductor belt or film on a film core is exposed to an image at one location and transfers the toned image to a receiver at another location, it is essential that the belt track accurately with very little lateral drifting movement, so that only very small corrections are required to maintain the belt within a predetermined path; particularly if two or more images are to be superimposed, as in the case of color copying. However, controlling the lateral position of the belt by having it simply abut along one edge with a roller flange or other constraining member is not desirable, because of wear to the belt edge and, because, in such a system, the accurate tracking of the belt is dependent on the accuracy of the edge itself, which is difficult to establish and maintain. Accordingly, many film cores include a steering roller that is pivotable about a steering axis intersecting the center of the roller axis and the portion of the belt partially wrapped around the roller. A belt sensor detects the lateral position of the corresponding edge of the belt and actuates a servo system that pivots the steering roller about its steering axis to control the path of the belt, thereby keeping the belt within a predetermined "dead band" range of lateral positions. The sensor and the servo system can be entirely mechanical or can comprise various combinations of mechanical, electrical, optical, hydraulic or other types of sensors and servo devices.
In the prior art, various structures are employed for providing for the steering movement of the steering roller relative to one or more other rollers or other web supporting elements of the film core. For example, as shown in U.S. Pat. No. 3,796,488 or U.S. Pat. No. 3,801,092, the steering roller can be supported in a yoke that is connected to a rigid frame of the film core by a pivotally supported spindle that defines the steering axis. Alternatively, the side members of the frames that support the steering roller can be pivotally mounted, as shown in U.S. Pat. No. 3,435,693. Yet another alternate approach is to support the steering roller to the rigid frame of the film core by means of one or more flexure members that are flexible to allow pivoting movement of the roller about its steering axis, but which prevent other rotational or translational movements of that roller, other than its rotation about its own axis.
All of the foregoing approaches to defining the pivot axis of the steering roller have advantages and disadvantages but, in common to all of them, is the fact that additional components must be attached to the film core frame to provide for the steering movement of the steering roller.